Shell Fired by ISIS at U.S. and Iraqi Troops May Have Contained Chemical Agent

WASHINGTON — Fighters with the Islamic State fired a shell onto a military base in northern Iraq, home to American and Iraqi troops, that may have contained a chemical agent, military officials said on Wednesday.

The shell did not explode, and the officials said no American or Iraqi troops were injured in the attack.

The soldier who brought the shell in for testing has not shown any blistering in the 24 hours since handling it, said the military officials, who spoke on condition of anonymity because they were not authorized to discuss the situation.

While the unexploded shell initially tested positive for a mustard agent, a second test was negative. Additional tests have been ordered.

The attack, which was first reported by CNN, occurred at a base being used to prepare Iraqi forces for the offensive to retake Mosul from the Islamic State.

Defense Department officials said that in the past few months Islamic State fighters have fired several shells containing mustard agents at Iraqi, Kurdish and American troops, and said the attacks generated a “moderate level of concern on a day-to-day basis.”

Last summer, the Islamic State used chemical agents — again, mustard gas — in an attack on Kurdish fighters in northern Syria; and Kurdish news media outlets reported another mustard gas attack a few weeks later on Kurdish fighters in Makhmur, Iraq.